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Originally, the term nori was generic and referred to seaweeds, including hijiki.[1] One of the oldest descriptions of nori is dated to around the 8th century. In the Taihō Code enacted in 701, nori was already included in the form of taxation.[2] Local people have been described as drying nori in Hitachi ProvinceFudoki (721–721), and nori was harvested in Izumo ProvinceFudoki (713–733), showing that nori was used as food from ancient times.[3] In Utsubo Monogatari, written around 987, nori was recognized as a common food. Nori had been consumed as paste form until the sheet form was invented in Asakusa, Edo (contemporary Tokyo), around 1750 in the Edo period through the method of Japanese paper-making.[4][5][6][7]

The word "nori" first appeared in an English-language publication in C.P. Thunberg's Trav., published in 1796.[8] It was used in conjugation as "Awa nori", probably referring to what is now called aonori.[8]

The Japanese nori industry was in decline after WWII, when Japan was in need of all food that could be produced. The decline was due to a lack of understanding of the plant's three-stage life cycle so that local people did not understand why traditional cultivation methods were not effective. The industry was rescued by knowledge deriving from the work of British phycologistKathleen Mary Drew-Baker, who had been researching the organism Porphyria umbilicalis, which grew in the seas around Wales and was harvested for food, as in Japan. Her work was discovered by Japanese scientists who applied it to artificial methods of seeding and growing the plants, rescuing the industry. Kathleen Baker was hailed as the "Mother of the Sea" in Japan and a statue erected in her memory; she is still revered as the savior of the Japanese nori industry.

In the 21st century, the Japanese nori industry faces a new decline due to increased competition from seaweed producers in China and Korea and domestic sales tax hikes.[9]

The word nori started to be used widely in the United States, and the product (imported in dry form from Japan) became widely available at natural food stores and Asian-American grocery stores in the 1960s due to the macrobiotic movement[10] and in the 1970s with the increase of sushi bars and Japanese restaurants.[11]

In one study by Jan-Hendrik Hehemann, subjects of Japanese descent have been shown to be able to digest the polysaccharide of the seaweed, after gut microbes developed the enzyme from marine bacteria. Gut microbes from the North American subjects lacked these enzymes.[12]

Production and processing of nori is an advanced form of agriculture. The biology of Pyropia, although complicated, is well understood, and this knowledge is used to control the production process. Farming takes place in the sea where the Pyropia plants grow attached to nets suspended at the sea surface and where the farmers operate from boats. The plants grow rapidly, requiring about 45 days from "seeding" until the first harvest. Multiple harvests can be taken from a single seeding, typically at about ten-day intervals. Harvesting is accomplished using mechanical harvesters of a variety of configurations. Processing of raw product is mostly accomplished by highly automated machines that accurately duplicate traditional manual processing steps, but with much improved efficiency and consistency. The final product is a paper-thin, black, dried sheet of approximately 18 cm × 20 cm (7 in × 8 in) and 3 grams (0.11 oz) in weight.

Several grades of nori are available in the United States. The most common, and least expensive, grades are imported from China, costing about six cents per sheet. At the high end, ranging up to 90 cents per sheet, are "delicate shin-nori" (nori from the first of the year's several harvests) cultivated in Ariake Sea, off the island of Kyushu in Japan.[13]

In Japan, over 600 square kilometres (230 sq mi) of coastal waters are given to producing 350,000 tonnes (340,000 long tons) of nori, worth over a billion dollars. China produces about a third of this amount.[14]

Nori is commonly used as a wrap for sushi and onigiri. It is also a garnish or flavoring in noodle preparations and soups. It is most typically toasted prior to consumption (yaki-nori). A common secondary product is toasted and flavored nori (ajitsuke-nori), in which a flavoring mixture (variable, but typically soy sauce, sugar, sake, mirin, and seasonings) is applied in combination with the toasting process.[15] It is also eaten by making it into a soy sauce-flavored paste, nori no tsukudani (海苔の佃煮).

Nori is sometimes used as a form of food decoration.

A related product, prepared from the unrelated green algae Monostroma and Enteromorpha, is called aonori (青海苔 literally blue/greennori) and is used like herbs on everyday meals, such as okonomiyaki and yakisoba.

Since nori sheets easily absorb water from the air and degrade, a desiccant is indispensable when storing it for any significant time.

While seaweed has by far the highest proportion of iodine by weight of any food,[16]Pyropia yezoensis has less than any other type of seaweed; it is nonetheless an excellent source of iodine.[17]

Though nori has long been considered to be an important source of vitamin B12 for vegans,[18][19] its vitamin B12 may actually not be biologically available to humans. It may contain cobalamin analogues which block absorption of B12.[20][21] A study showed that in humans both dried and raw nori reduced the vitamin B12 status.[22][23]

^Kodansha encyclopedia of Japan. 6. Kōdansha. 1983. p. 37. ISBN0-87011-620-7. The word nori is used in Japan both as a general term for seaweed and as a name for a species of red algae (Pyropia tenera) that is commonly used as a foodstuff and is also known as asakusa-nori.

^Nisizawa, Kazutosi; Noda, Hiroyuki; Kikuchi, Ryo; Watanabe, Tadaharu (September 1987). "The main seaweed foods in Japan". Hydrobiologia. 151-152 (1): 5–29. doi:10.1007/BF00046102. Retrieved 25 March 2013. In the Law of Taiho (AD 701) which was established by the Emperor at that time, marine algae such as Laminaria, Undaria and its sporophyll, Pyropia and Gelidium are included among marine products which were paid to the Court as tax.

^Shimbo, Hiroko (2001). The Japanese kitchen: 250 recipes in a traditional spirit. Harvard Common Press. p. 128. ISBN1558321772. Unlike wakame, kombu, and hijiki, which are sold in the form of individual leaves, nori is sold as a sheet made from small, soft, dark brown algae, which have been cultivated in bays and lagoons since the middle of the Edo Era (1600 to 1868). The technique of drying the collected algae on wooden frames was borrowed from famous Japanese paper-making industry.

^"How can I safely consume seaweed?". Examine.com. It is relatively easy to consume most seaweeds safely, but high intakes of raw kelp (kombu, or any seaweed starting with Laminaria) are a very significant concern for iodine toxicity. For daily kombu intake, proper cooking techniques should be followed for safety.